1. Field of the Invention
The present invention relates generally to superconducting oxide films and processes for forming thick films of superconducting oxide films. More particularly, the present invention is directed to a electrodeposition process where oxygen is bubbled into the electrolyte during deposition to deposit superconductor precursors onto a wide variety of substrates for subsequent annealing for production of superconducting oxide films. The present invention is further directed to a process of preparing superconducting oxide films from annealed multilayered precursors, wherein the precursor comprises two or more separately electrodeposited layers and wherein an intermediate Ag layer is deposited between each electrodeposited layer. The electrodeposited layers in the multilayered precursors are deposited from an electrolyte solution, which may or may not be saturated with oxygen.
2. Description of Related Art
There has been a great deal of effort expended in designing and developing suitable processes for making superconducting oxide films. The most desirable of such processes are those that are simple, efficient, and capable of producing a superconducting oxide film with a relatively high superconducting transition temperature (T.sub.c) Processes which employ electrodeposition as part of the superconductor fabrication procedure have been proposed due to the simplicity, reproducibility, and coating quality that can be obtained using electrodeposition techniques. The deposition processes used to form superconducting oxide films typically involve electroplating a mixture of the desired metals onto a suitable surface to form a film of superconducting precursor metals, which is then annealed at high temperature to form the superconducting oxide. Various methods have been used for the preparation of superconductors. One such general methodology for preparing superconducting oxide films comprises the electrochemical deposition of a mixture of appropriate metals on a substrate, followed by oxidation of the deposited, mixture into the superconducting oxide film. A related method comprises the sequential electrodeposition of layers of appropriate metals on a substrate, followed by oxidation of the deposited, layers. Another approach involves suspending, dispersing or dissolving superconductor precursor components within a liquid medium, followed by electrodeposition on a substrate and subsequent oxidation of the entire mass. Exemplary electrodeposition procedures are set forth in the following U.S. Pat. Nos.: 4,870,051; 4,879,270; 4,939,308; 5,120,707; and 5,162,295. The superconducting oxide films may be prepared on various substrates, including wires or tapes, depending on the desired use of the superconducting oxide film.
The primary technical challenge that must be satisfied to permit usage of high temperature superconducting (HTS) wires or tapes in superconducting magnets or power-related applications is the successful demonstration of a low-cost, high-field, high current-carrying wire or tape with acceptable mechanical properties. A great deal of effort has recently been directed to the use of YBa.sub.2 Cu.sub.3 O.sub.7-x (YBCO). YBCO has useful magnetic properties at 77 K, but it is highly susceptible to magnetic field degradation in the transport current due to weak links resulting from high-angle grain boundaries.
Thallium (Tl)-based superconducting oxide films present an alternative to YBCO due to a number of features, including high transition temperatures reaching to 127 K and unique features in their growth morphology. Nabatame et al. Physica C (1992) 193: 390) reported a magnetic field versus temperature irreversibility line for a thallium-based superconducting oxide that compared favorably at 77 K with the YBCO performance.
Although many of the previously-developed deposition procedures are suited for their intended purposes, there is still a continuing need to develop further and even better deposition procedures that are simple, efficient, and capable of producing superconducting oxide films that have relatively high superconducting transition temperatures. There is also a continuing need to develop efficient deposition procedures for producing thick superconducting oxide films having good film morphology and the are suitable for use in superconducting magnets and other power related applications.